At the time of his death, Russia's RIA Novosti news agency, citing family members, reported that the 57-year-old former press minister had died from a heart attack in his room at Washington's Dupont Hotel on Nov. 5.

Russian Foreign Ministry spokeswoman Maria Zakharova wrote on Facebook after news broke that the Russian embassy "has repeatedly sent through diplomatic channels inquiries about the progress of the investigation into the death of Russia's citizen."

"The U.S. side has not provided us any substantive information," she added.

The Dupont Circle Hotel in Washington, where Mikhail Lesin was found dead, Saturday, Nov. 7, 2015.

Image: AP Photo/Andrew Harnik

The circumstances of his death, including the location — the U.S. capital — have fueled conspiracy theories and led to speculation that he was murdered after offering help to American authorities.

"Litvinenko-Perepilichny-Berezovsky-Lesin. Who else?" Tikhon Dzyadko, a Russian journalist at the independent TV Rain channel, tweeted Thursday. He was referring to a string of high-profile deaths of powerful Russians in London and Washington.

Who was Mikhail Lesin?

Mikhail Lesin, right, looks over documents with a colleague during a meeting headed by Russian President Vladimir Putin, at the Kremlin in Moscow, Aug. 28, 2000.

Image: AP

Lesin, an influential media mogul in Russia, was a controversial figure who provoked the ire of the West, and U.S. Senator Roger Wicker in particular.

The Mississippi Republican in 2014 alleged Lesin was the mastermind behind the Kremlin's crackdown on Russia's independent television outlets and even called on the Justice Department to launch an investigation into accusations of corruption and money laundering.

Lesin had procured $28 million worth of property in Los Angeles and "multimillion dollar assets in Europe" during his time as a civil servant, which "raises serious questions," Wicker said at the time.

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